Fanconi Anemia (FA) is a complex autosomal recessive disease whose hematologic manifestations are characterized by a progressive and ultimately fatal hypoplastic anemia, hypersensitivity to clastogenic agents such as mitomycin C (MMC), chromosomal breaks and a markedly increased incidence of acute myelogenous leukemia. There are five known complementation types of FA (A-E). Type A is the most common and is estimated to account for 50-60% of all patients. Our previous investigations have shown that ribosomal protein S3 is a multifunctional protein having DNA repair capabilities acting on acting as a combined DNA glycosylase/AP lyase recognizing 8-oxoguanine lesions formed in DNA during normal oxidative metabolism. FA-A cells have been shown to have elevated 8-oxoguanine levels in their DNA. Using the Drosophila S3 cDNA, we have found that S3 complements the FA-complementation type A cells back to wild type levels when challenged with the DNA damaging agent MMC. We propose to: 1) Determine if S3 can complement the MM sensitivity of the other FA types and whether S3 can also complement the hydrogen peroxide (oxidative damaging agent) sensitivity of the FA-A cells, along with the other FA types, 2) sequence cDNAs from the FA-A cells to determine if a primary defect exists in the coding region of S3, 3) alter the nuclear localization signal of S3 and determine this effect on S3's ability to complement FA-A, and 4) determine whether glycosylation or phosphorylation of S3 is responsible for S3 trafficking and its nuclear or ribosomal localization and, therefore, its ability to complement FA-A. We feel these findings will be of significant importance in the understanding of the FA-A DNA repair defect phenotype.